SecurityContextHolder.getContext().setAuthentication() 认证逻辑?

Spring Security认证 是否是从Authentication对象的属性去判断请求经过认证了?我在以下代码中authenticationToken 构造参数全部设置为空,为什么拦截需要认证的请求 可以通过认证

UsernamePasswordAuthenticationToken authenticationToken =
                new UsernamePasswordAuthenticationToken(null, null, null);
        SecurityContextHolder.getContext().setAuthentication(authenticationToken);
        filterChain.doFilter(request, response);